IMPROVED METHODS FOR FAT ANALYSIS. 121 



Neutralization : — 



RCOOH +ROCO + (RCO) 2O +KOH = RCOOK +ROCO + (RCO) 2O +H2O 

 acid lactone anhydride 



Saponification: — 



RCOOH+ROCO + (RCO)20+4 KOH 



=RCOOK+R . OH . COOK +2 RCOOK +2 H=0 



When the lactone or anhydride in the insoluble acids, or the predomi- 

 nant one in a mixture, is known, the percentage (L) can be calculated from 

 the determined alkali equivalent^ (1), — i.e., saponification number less 

 acid number of insoluble acids, and the theoretical saponification number 

 (k) of the lactone or anhydride, — by the formula — 



L = J 



k 



Iodine Number. 



The iodine number indicates the percentage of iodine chloride absorbed 

 under definite conditions by the insoluble fatty acids, expressed in terms 

 of iodine. 



See method for oils and fats. 



The iodine number of insoluble acids does not necessarily correspond 

 to that of the natural oil, fat or wax from which the acids were derived. 

 This is said to be due to the influence of soluble fatty acids in the natural 

 product, although it is probable that in the process of separation some 

 decomposition of the unsaturated acids results. 



Insoluble acids after titration with thiosulfate undergo a reversible 

 reaction and spUt off iodine much more rapidly than the oils and fats 

 from which thej'' were derived. 



Acetyl Number. 



The acetyl number indicates the number of milligrams of potassium 

 hydroxide required to combine with the acetyl absorbed by 1 gram of 

 insoluble fatty acids on acetylation. 



See method for oils and fats. 



The acetylated product should be washed until the acidity of the fil- 

 trate (150 cubic centimeters) is less than 0.25 cubic centimeter N/10 

 solution. 



Stearic Acid. 



The stearic acid indicates the percentage of that acid in the insoluble 

 fatty acids of an oil or fat. 



Reagents. — Alcoholic-stearic solution: 3 grams of crystalline stearic 

 acid of theoretical molecular weight to 1,000 cubic centimeters of purified 



' Lactone number. 



